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(1856–1940)

British physicist, who was awarded the 1906 Nobel Prize for Physics for his discovery of the electron in 1897. He was knighted in 1908.

The son of a bookseller and publisher, Thomson was educated at Owens College in his home town of Manchester and Trinity College, Cambridge, where he studied mathematics. He remained in Cambridge working at the Cavendish Laboratory under Lord Rayleigh (1842–1919), whom he succeeded as Cavendish Professor of Experimental Philosophy in 1884. Thomson remained at the Cavendish until he was succeeded by his pupil Ernest Rutherford in 1919, when he himself was appointed master of Trinity College.

By passing cathode rays through evacuated discharge tubes, Thomson identified a particle that could be deflected by both electric and magnetic fields. He went on to measure the ratio of the particle's charge to its mass and found it to be considerably higher than that worked out for light atoms. The new particle was given the name ‘electron’. Thomson's work was reported in his Conduction of Electricity Through Gases (1903). Having identified the electron Thomson went on to explore the nature of ‘positive rays’ (protons), work he described in his Rays of Positive Electricity. Not the least of Thomson's achievements after 1900 was the Cavendish Laboratory itself. Seven of his pupils won Nobel Prizes, fifty-five became professors, and the Cavendish became the leading laboratory in the world for research in atomic physics. He was buried in Westminster Abbey close to his Trinity College predecessor, Sir Isaac Newton, and his Cavendish successor, Lord Rutherford.